The invention relates to improvements in methods of and in apparatus for making continuous rods which can be subdivided into cigarettes, cigars, cigarillos, filter rod sections and analogous rod-shaped articles of the tobacco processing industry. More particularly, the invention relates to improvements in methods of and in apparatus for draping rod-like fillers of natural, reconstituted and/or substitute tobacco, filter material for tobacco smoke and/or other fibrous material of the tobacco processing industry into webs of cigarette paper, filter paper, imitation cork, tipping paper or other suitable wrapping material to form continuous rods of the tobacco processing industry. Still more particularly, the invention relates to improvements in methods of and in apparatus for enhancing the quality of customary seams which are formed by overlapping marginal portions of webs of wrapping material as a result of draping such webs around rod-like fillers of smokable material or filter material for tobacco smoke.
A continuous web of cigarette paper, filter paper or the like is provided with a film or coat of suitable adhesive on its way toward or at the wrapping station where successive increments of the web are draped around successive increments of a continuous rod of smokable material or filter material for tobacco smoke. The applied adhesive serves to bond the overlapping marginal portions of the draped web to each other in order to prevent opening of the seam during further treatment of the rod, e.g., during subdivision of the rod into rod-shaped articles of unit length or multiple unit length. In many instances, the film of adhesive is applied, by a so-called paster, to one marginal portion at one side of the web while the web advances toward or at the wrapping station. The adhesive-coated marginal portion is folded over and bonded to the other marginal portion during passage through and downstream of the wrapping mechanism. The thus obtained seam extends in parallelism with the axis of the finished rod.
The rod-like filler which is to be draped into a web of wrapping material can constitute a one-piece body of shredded or otherwise comminuted particles of smokable material or a one-piece body of fibrous filter material, such as a tow of acetate fibers which are contacted by a softening agent. Reference may be had, for example, to U.S. Pat. No. 3,769,883 granted Nov. 6, 1973 to Greve for "Apparatus for regulating the operation of filter rod making machines". However, it is equally possible to drape a rod-like filler consisting of a file of discrete rod-like sections which are or can be disposed end to end. See, for example, commonly owned U.S. Pat. No. 4,010,678 granted Mar. 8, 1977 to Greve et al. for "Method and apparatus for making composite filter plugs".
The adhesive which is used in tobacco rod making or filter rod making machines is often a hotmelt. However, it is equally known and possible to use other types of adhesive substances such as dispersion type glue, starch-containing glue and/or others.
The quantity of applied adhesive should be selected in such a way that it suffices to ensure the establishment of a reliable bond between the overlying marginal portions of the draped web before the rod is subdivided into sections of unit length or multiple unit length. On the other hand, the quantity of applied adhesive should not be excessive because the surplus is likely to issue from the seam and contaminate, and thus affect the appearance of, the external surface of the tubular wrapper of the finished rod. Accurate metering of the applied quantities of adhesive does not present many problems if the paster is located close or very close to the locus where the marginal portions of the draped web are caused to contact each other in the wrapping mechanism. However, the positioning of a satisfactory paster into close or immediate proximity to the wrapping station is not always possible, either for structural reasons, due to lack of adequate space and/or on other grounds. In such rod making machines, the paster must be installed adjacent the path of advancement of the web toward the wrapping mechanism, i.e., upstream and often well ahead of the wrapping station. This can create numerous and serious problems in connection with the application of satisfactory quantities of adhesive per unit area or unit length of the web, particularly since the speed of advancement of the web must be variable to thus ensure proper acceleration of the web during starting or restarting of the machine, proper deceleration of the web while the machine is in the process of being brought to a halt, and proper deceleration of the web in response to malfunctioning of the machine, for the purposes of inspection, for testing and/or for other reasons. Thus, if the speed of the web is reduced below or substantially below the nominal speed in a rod making machine wherein the paster is located well upstream of the wrapping station, the applied film or layer of adhesive is likely to set, at least in part, on its way from the paster to the wrapping station so that the seam of the tubular envelope forming part of the finished rod is not adequately closed and sealed and permits the inflow of atmospheric air and/or the escape of smoke when an article embodying or consisting of a portion of such defective rod is lighted.
Attempts to overcome the just enumerated problems in rod making machines wherein the paster discharges hotmelt include the provision of a heating device in the wrapping mechanism proper. Such heating device raises the temperature of and thus reactivates the hotmelt just before or while the adhesive-coated marginal portion of the web is caused to contact the other marginal portion. The provision of a heating device at the wrapping station contributes to complexity and to the cost of such mechanism and of the entire rod making machine. Moreover, reheating of hotmelt at the wrapping station renders it necessary to enhance the effectiveness of the cooling unit which is located downstream of the wrapping station and acts upon the freshly formed increments of the seam in order to promote rapid setting of hotmelt and to thus ensure reliable bonding of the overlying marginal portions of the draped web to one another.